Explosion gas operated piston-cylinder structure

ABSTRACT

A piston-cylinder drive structure particularly for use in actuating electric switchgear apparatus comprises a cylinder into which explosion gases are admitted for actuating a piston located in the cylinder. Rather than having a uniform cross-sectional area, the cross-section of the cylinder is progressively increased in the direction of piston travel and the piston includes means for effecting a like increase in its crosssectional area as it is actuated and maintains its engagement with the cylinder wall. The result is a more favorable forcetravel characteristic resulting in practically a constant pressure throughout the piston travel for the switchgear drive notwithstanding a progressively decreasing gas pressure concurrent with a progressively increasing volume within the cylinder.

United States Patent Strubin Sept. 30, 1975 EXPLOSION GAS OPERATED3.502.002 3/1970 Whiteman, Jr. 91 402 x PISTON'CYUNDER STRUCTURE FOREIGNPATENTS OR APPLICATIONS 1 lm'cmorl f Strum", Fislisbach 21,854 4 1907United Kingdom 92/240 swltzerland 1,168,234 12/1958 France 92 194 [73]Assignee: BBC Brown Boveri 8L Company Li it d, B d S i l d PrimaryE.\an1inerMartin P. Schwadron 7 I Assistant Examiner-Abraham HershkovitzFlled' June 1973 Attorney, Agent, or Firm-Pierce, Scheffler & Parker[211 App]. No.: 369,248

[57] ABSTRACT Foreign Application Priorily Data A piston-cylinder drivestructure particularly for use July l2, l972 Switzerland 10352/72 inactuating electric switchgear apparatus comprisesfa cylinder into whichexplosion gases are admitted for [52] US. Cl 91/357; 92/6 R; 92/89;actuating a piston located in the cylinder. Rather than 92/169; 92/193;92/247 having a uniform cross-sectional area, the cross- [5 l Int. Cl.F15B 9/02 section of the cylinder is progressively increased in the [58]Field of Search 92/6 R, 6 D, 89, 169, 193, direction of piston traveland the piston includes 92/194, 247, 240; 91/394, 357, 402 means foreffecting a like increase in its crosssectional area as it is actuatedand maintains its en- [56] References Cited gagement with the cylinderwall. The result is a more UNITED STATES PATENTS favorable force-travelcharacteristic resulting in prac- 5/1918 Hudford X tically a constantpressure throughout the piston travel 2:554:55; 8,194. Berr....1IIIIIIIIIII1IIIII11111111927194 x fee ehe eweeheeee driveneewieheemeieg 1430493 11/1947 Carbon 93/194 X sively decreasing gaspressure concurrent with a pro- 2,7l0.077 6/1955 Fabel et al. 92/193 Xgressively increasing volume within the cylinder. 3,111.808 11/1963Fritz 92/169 X 3.245.591 4/l966 Kneusel et a1. 92/6 R x w 1 Clalme 2Drawing Flgures u, N g) 13 j EXPLOSION GAS OPERATED PISTON-CYLINDERSTRUCTURE This invention relates to an improvement in a drive apparatusof the type in which a piston is displaced in a cylinder by explosionofa charge, in particular for operating electrical switchgear.

Electrical switching devices with so-called explosion drives are knownwhere the drive is of such a form that a drive piston is located in acylinder of circular crosssection such as described in Germanspecification published June 15, 1972, for example. Drives of this kindexhibit an unfavorable displacement characteristic, accompanied by highmaterial stresses, because owing to the very high combustion rate of thepropellant charge the duration of combustion is much shorter than themechanical travel time suitable and acceptable for most electricalswitching devices. Furthermore, if the size of the propellant charge iswithin economically tolerable limits the volume of gas resulting fromthe explosion is relatively small, and therefore, owing to the increasein volume of the drive chamber as the piston is displaced, the pressureof the gases in the chamber falls off very rapidly during the mechanicalmovement.

The principal object of the invention is to provide a solution such thatthe pressure and piston displacement are better matched to each other,resulting in a more favorable force/travel characteristic, e.g.,practically constant pressure throughout the piston travel, for thedrive apparatus described above. This objective is achieved in that thecylinder chamber is of rectangular cross-section, the cross-section areaincreasing progressively in the direction of piston travel, and that thepiston which likewise increases in area incorporates means whereby aseal, at least quasi-leakproof, is maintained between the piston and theinner cylinder wall during the mechanical movement.

A preferred embodiment of the invention is illustrated in theaccompanying drawing, in which:

FIG. 1 is a sectional elevation of the drive apparatus, and

FIG. 2 is a cross-section through the apparatus at line AA and viewed inthe direction of the arrows.

With reference now to FIG. 1, the drive piston 1 is located in cylinderchamber 2. The latter is of rectangular cross-section increasingprogressively in area in the direction of piston displacement. For thispurpose a conical housing 3 contains four segment-shaped elements 2a to2d. The cylinder chamber 2 thus has two wedge-shaped and two parallelbounding surfaces, the former being formed by elements 20, 2d and thelatter by elements 2a, 2b. The housing 3 is enclosed at one end by aflanged cover 4 through which the piston rod 1a of piston 1 passes. Atthe opposite end of the housing is an opening 5 through which theexplosion gases are admitted. Connected to the opening 5 is a combustionchamber, not described in further detail, with an ignition device andsupply of explosion propellant. The head of piston l subjected to theexplosion gases and which is expandable in area when moving in thedriven direction comprises two flaps 6 which are pivoted about studs 7to establish the increasing cross-sectional area character of the pistonthat matches the increasing cross-sectional area of the explosionchamber. In the lower. fully withdrawn, end position, i.e., the startingposition of the piston, the flaps 6 are pressed at their lower roundedends by spring 8 into sealing engagement against elements 20, 2d. Theflaps 6 are sealed along their sides relative to elements 2a, 2]; bypieces 10, e.g., of steel, inserted in corresponding slots. To press thepieces 10 against the parallel surfaces of elements 2a, 2b, springdevices, e.g., corrugated spring strips 9, can be inserted betweenpieces 10 and the base of the slots, as shown in more detail in FIG. 2.At the top in the vicinity of the pivot axes the flaps 6 are sealedrelative to one another by a steel element 11 which fills theintervening space.

The explosion gases created when a propellant charge is ignited are fedthrough the opening 5 and displace the piston l to its upper extremeposition, indicated by the broken line. In this manner the electricalswitching device, connected in known fashion with the piston rod 1a andnot further described, is moved in the desired direction. During thismovement the flaps 6 are pressed also by the gas pressure againstelements 20. 2d in addition to the force of spring 8. At the same timethis has the effect of progressively increasing the effective pistonsurface area, and as a result the driving force remains practicallyconstant, despite the decreasing pressure owing to the increasing volumeof the chamber. The discharge ports 12 in the segment shaped elements2a, 2b open at or shortly before the upper end position as they arepartly uncovered by the expandable piston head as shown by the brokenline position of these flaps in FIG. 1 so that the explosion gases canescape through ports 12 and the openings 13 in flange cover 4. If theswitching device is also to be driven in the opposite direction by driveapparatus of the kind proposed, one such apparatus is provided for eachdirection, the one being returned to its starting position by the other.

I claim:

1. A piston-cylinder drive structure for use in actuating electricswitchgear apparatus comprising a cylinder including a conical housingcontaining two pairs of oppositely disposed segment-shaped elementsestablishing a working chamber for explosion gases admitted through aninlet at the smaller end of the housing, a first pair of saidsegment-shaped elements establishing a pair of oppositely disposedwedge-shaped bounding surfaces and a second pair of said segment-shapedelements establishing a second pair of oppositely disposed parallelbounding surfaces which together establish a working chamber having arectangular cross-section and whose area progressively increases in thedrive direction of the piston travel from the explosion gas inlet end, adrive piston within said working chamber, said drive piston including apiston rod extending through the larger end of said housing and havingan areaexpandable head slidable in contact with the said boundingsurfaces of said chamber from the smaller to the larger area end inresponse to the pressure of the explosion gases, said piston headcomprising two pivotally mounted flaps and spring means cooperabletherewith and which serve to maintain said flaps in sealing contact withsaid pair of wedge-shaped bounding surfaces, the sides of said pivotallymounted flaps in contact with said second pair of oppositely disposedparallel bounding surfaces including slots containing spring-loadedsealing strips which function as piston seals with respect to saidparallel bounding surfaces, and at least one of said second pair ofsegment-shaped elements including a port for discharge of spent gasestherethrough into the larger end of said housing and thence through anescape opening therein into the surrounding atmosphere, said spent gasdischarge port being uncovered by said piston when it reaches the end ofits working stroke.

1. A piston-cylinder drive structure for use in actuating electricswitchgear apparatus comprising a cylinder including a conical housingcontaining two pairs of oppositely disposed segment-shaped elementsestablishing a working chamber for explosion gases admitted through aninlet at the smaller end of the housing, a first pair of saidsegment-shaped elements establishing a pair of oppositely disposedwedge-shaped bounding surfaces and a second pair of said segment-shapedelements establishing a second pair of oppositely disposed parallelbounding surfaces which together establish a working chamber having arectangular cross-section and whose area progressively increases in thedrive direction of the piston travel from the explosion gas inlet end, adrive piston within said working chamber, said drive piston including apiston rod extending through the larger end of said housing and havingan areaexpandable head slidable in contact with the said boundingsurfaces of said chamber from the smaller to the larger area end inresponse to the pressure of the expLosion gases, said piston headcomprising two pivotally mounted flaps and spring means cooperabletherewith and which serve to maintain said flaps in sealing contact withsaid pair of wedge-shaped bounding surfaces, the sides of said pivotallymounted flaps in contact with said second pair of oppositely disposedparallel bounding surfaces including slots containing spring-loadedsealing strips which function as piston seals with respect to saidparallel bounding surfaces, and at least one of said second pair ofsegment-shaped elements including a port for discharge of spent gasestherethrough into the larger end of said housing and thence through anescape opening therein into the surrounding atmosphere, said spent gasdischarge port being uncovered by said piston when it reaches the end ofits working stroke.